1. Field of the Invention
The present invention relates to a support structure for the rotary drive shaft of a reciprocating-piston type compressor such as a swash plate type compressor.
2. Description of the Related Art
In a reciprocating-piston type compressor, a swash plate rotates together with a rotary drive shaft for causing a plurality of pistons to reciprocate in their respective cylinder bores compressing refrigerant gas supplied into the cylinder bores from an eternal source. During this compressing process, a thrust load based on a compressive force acts on the drive shaft via the pistons and the swash plate. This compressive force causes the drive shaft to rotate with an irregular axial and radial displacement, resulting in excessive vibration rattling, shortening of life of compressor, etc.
Conventional compressors typically utilize a spring to apply a pre-load force to the drive shaft that counters the thrust load acting on the drive shaft. With such a construction, however, the magnitude of the thrust load acting on the drive shaft varies in accordance with the cooling load and other loads effecting the compressor, etc. Since this pre-load force counters that of the thrust load that acting on the drive shaft, the magnitude of the pre-load force is usually preset to a value greater than the maximum value of the thrust load. In an operation under a small cooling load where a small thrust load acts on the drive shaft, the pre-load force is typically and unnecessarily large. Consequently, the shaft receives an excess load, causing power loss in the compressor.
The magnitude of the pre-load force applied to the shaft may also be affected by variation in the manufacturing tolerances of the spring, such as size, spring force, etc. These variation constitutes to deviation in the pre-load force actually applied to the drive shaft. This, in effect, contributes to the tendency of the conventional compressor to experience power loss and a rattling of the drive shaft in the compressor due to an excessive pre-load force.